The prior art provides several types of filters for use with radio frequency signals including high pass, low pass, band pass, notch and other types of filters fabricated in lumped or distributed form. Filters of these types have been formed in a variety of transmission media.
To accommodate higher frequency signals some filters have been fabricated in microstrip transmission media using distributed elements. Microstrip transmission media generally consists of one or more thin conducting strips of finite width that are arranged parallel with a single extended conducting ground plan. In its common form, the strips are fixed to one side of an insulating substrate and the ground plane is attached to the other side. While microstrip transmission media have been recognized as possible conductors for higher frequency signals, microstrip transmission media also have disadvantageous aspects. These aspects include that the fabrication of microstrip circuits is process intensive, involving (1) metalization on two sides of a substrate and (2) the formation of interconnecting vias between the two surface materialization layers to achieve proper grounding.
Coplanar waveguide (CPW) and slot line are alternative types of transmission media. Both CPW and slot line support uniplanar fabrication, though they have not been used widely for high frequency signal propagation.
To provide less expensive and more efficient circuit construction, a need exists to form circuits that support high frequency operation (approximately &gt;1 GHz) in a uniplanar transmission media. To provide necessary signal processing, a need exists to provide circuit components such as band reject filters and the like in such media. Suitable band reject filters will provide LO, image reject and spurious frequency filtering.